1. Field of the Invention
This invention relates to a printer, and more particularly to a process for setting a printing sheet, especially an individual or cut paper, form, or sheet, hereinafter referred to as "cut sheet", which is prevented from being inclined when inserted into the printer and set in a proper print start position.
2. Description of the Related Art
A cut sheet printer usually comprises a cylindrical platen and a pinch roller resiliently in contact with the platen. After a cut sheet is loaded on the printer, the platen is rotated by a line feed controller according to an instruction for feeding the cut sheet. Therefore, the platen cooperates with the pinch roller to feed the cut sheet in the forward direction along a sheet transport passage having a guide member. A sheet sensor is provided, along the sheet transport passage, by which the presence of the sheet is confirmed. When the sheet is fed by a given distance after the sheet sensor detects a front of leading edge of the sheet, the platen is stopped to set the sheet at a print start position.
If, however, the sheet was inclined while being transported, printing would not properly be carried out. That is, the printing would be carried out along an inclined transverse line, or the printing sheet might be crumpled or jammed. Therefore, it is important to prevent the printing sheet, especially a cut sheet, from being inclined.
To prevent a cut sheet from being inclined, it is known in the prior art that two sheet sensors 101A and 101B are provided in a sheet transport passage, as shown in FIG. 4. These two sensors 101A and 101B are arranged along a transverse line perpendicular to the feeding direction of the cut sheet 100. If the sheet 100 is inclined, as shown in FIG. 5, when one of the sensors 101A detects the sheet, the other sensor 101B does not detect the same. In such a printer known in the prior art, if a difference between the detection timings by these two sensors 101A and 101B exceeds a predetermined value, i.e., if the sheet is inclined, the sheet is discharged without being printed.
This printer can only discharge the printing sheet if inclined, but cannot correct the inclined sheet to a proper feeding state. Therefore, a printer having a means for automatically correcting an inclined sheet has long been desired.